None of the references described or referred to herein are admitted to be prior art to the claimed invention.
Nucleic acid-based assays and other reactions (e.g., chemical or biological) are frequently performed on automated, computer-controlled analyzers that include an automated fluid transfer apparatus configured to transfer fluids into and/or out of one or more receptacles by means of one or more fluid transfer probes. Each fluid transfer probe will typically be used to transfer fluids into and out of multiple different receptacles. Therefore, to prevent or limit cross-contamination between different receptacles accessed by the same fluid transfer probe, the fluid transfer probe is preferably covered during fluid transfer operations at its distal end by a protective conduit, such as a disposable tip. A tip is engaged by a fluid transfer probe prior to commencing fluid transfer with respect to a particular receptacle and is then discarded when fluid transfer is complete for that receptacle. Thus, residual fluid that may otherwise remain on the distal end of a fluid transfer probe, and get carried over into subsequent receptacles, i.e. cross-contamination, instead remains on the end of a tip and is discarded with the tip.
In an automated system, automated determinations of certain conditions or parameters affecting the fluid transfer apparatus must be made. For example automated determination of fluid level in the receptacle provides verification that the amount of fluid dispensed into or removed from the receptacle is correct. Automated confirmation of the presence of a tip on the fluid transfer probe ensures that a tip has been properly engaged prior to commencing fluid transfer for a particular receptacle. Similarly, automated confirmation of the absence of a tip at the end of the fluid transfer probe ensures that the tip has been properly discarded following the fluid transfer for the receptacle.
Known systems for detecting a fluid level within a receptacle in an automated analyzer include capacitive level sensing systems. In one implementation of such a system, the fluid transfer probe and the receptacle and its fluid contents comprise components of a system for which the electrical capacitance can be measured. When the probe contacts a fluid level surface within the receptacle, a measurable change of the capacitance occurs, so that contact with the fluid level surface can be detected.
The presence or absence of a protective tip on a fluid transfer probe can be detected by means of an optical detector. For example, the optical detector may comprise an emitter component and a detector component, and the fluid transfer probe can be moved into the optical path so as to place the protective tip between the emitter component and the detector component. If the tip is present, the optical path is blocked, and if the tip is absent, the optical path is unblocked.
The use of an optical detector to detect the presence or absence of a protective tip adds another layer of complexity to the fluid transfer apparatus, especially if the apparatus includes multiple fluid transfer probes, each of which requiring confirmation of the presence and absence of a protective tip. Furthermore, optical detectors are vulnerable to performance degradation due to dust or spillage on the emitter and/or detector component.